1. Technical Field
The present disclosure relates to an LED lighting apparatus, and more particularly, to a control circuit of an LED lighting apparatus, which is capable of reducing a flicker while performing lighting using a rectified voltage.
2. Related Art
According to the recent trend of lighting technology, LEDs have been employed as a light source in order to reduce energy.
A high-brightness LED is differentiated from other light sources in terms of various aspects such as energy consumption, lifetime, and light quality.
However, a lighting apparatus using LEDs as a light source may require additional circuits due to the characteristic of the LEDs which are driven by a constant current.
Examples of lighting apparatuses which have been developed to solve the above-described problem may include an AC direct-type lighting apparatus.
In general, the AC direct-type LED lighting apparatus is designed to rectify a commercial voltage and drive an LED using the rectified voltage which has a ripple twice larger than the commercial frequency.
Since the above-described AC direct-type LED lighting apparatus directly uses the rectified voltage as an input voltage without using an inductor and capacitor, the AC direct-type LED lighting apparatus has a satisfactory power factor.
Each LED of the LED lighting apparatus may be designed to be operated at 2.8V or 3.8V, for example. Furthermore, the LED lighting apparatus may be designed to be operated by a rectified voltage having a level at which a large number of LEDs connected in series can emit light.
As the ripple of the rectified voltage increases/decreases, a large number of LEDs included in the LED lighting apparatus may be sequentially turned on/off at each LED channel.
Since the rectified voltage which is supplied to drive the LED lighting apparatus has a ripple, the rectified voltage has a section in which it falls to such a level that the LED channels cannot emit light.
That is, the rectified voltage of the LED lighting apparatus substantially falls below the light emitting voltage of the LEDs due to the ripple. Thus, the current supplied to each LED channel has a section in which it falls below the lowest current and then rises.
When the entire LED channels are temporarily turned off, a flicker may occur. The flicker may degrade a feeling of use or increase the fatigue degree of a user.
Japan has defined a standard for the flicker levels of LED lighting apparatuses using a rectified voltage, based on the PSE standard. For example, the PSE standard of Japan has suggested a flicker level at which light output is sustained at 5% or more based on 100%, when a rectified voltage having a frequency of 100 Hz to 500 Hz is used to drive an LED.
Therefore, the LED lighting apparatus which is driven according to the rectified voltage characteristic needs to be designed to improve the flicker level.